Yasuhiro Nakasone, Japan's defense minister for 18 months from January 1970 and prime minister from 1982 to 1987, wrote in his memoir that he ordered the study after learning an official at the agency had researched the topic.
The Defense Agency team estimated it would take 200 billion yen (then worth US$570 million) and five years for Japan to arm itself with nuclear weapons, Nakasone wrote, according to Kyodo News. But since Japan had no testing ground for the weapons, the group decided development was unfeasible and the idea was abandoned, Nakasone wrote.
A copy of Nakasone's book, published by Tokyo-based Shinchosha Co., could not be immediately obtained. It was due for release June 25.
Japan is the only country to have suffered an atomic attack — the World War II bombings of Hiroshima and Nagasaki — and it has avidly campaigned to eliminate nuclear weapons, and is a strong backer of the Nuclear Nonproliferation Treaty.
The nuclear ambitions of North Korea have sparked a domestic debate in recent years on whether Japan should go nuclear, but the discussion has been mostly academic and the government has not seriously considered the idea.
Prime Minister Junichiro Koizumi has repeatedly reaffirmed Japan's policy banning the production, possession and transport of nuclear weapons.
Nakasone wrote that he has always rejected the development of nuclear weapons and has not changed his view, but that things "would be different if America stopped its nuclear defense of Japan.
"In that case, Japan would have to consider a variety of options, including whether to arm itself with nuclear weapons."